Question

public class Foo
{
    public ushort Weight { get; }
}

public class Bar<T> : IEnumerable where T : Foo
{
    private Collection<T> _contents;
    ...
    public ulong TotalWeight { get { return _contents.Sum(a => a.Weight); } }
}

I’m expecting the total to add up to more than the maximum value of a ushort.

I’m getting an Intellisense error: “Ambiguous Invocation”, with a list of numeric types that doesn’t include ushort or ulong. I’m not sure what it wants.

I also tried using Select (from this post), as follows:

_contents.Select(a => a.Weight).Sum()

but Intellisense complains that it cannot resolve the Sum method and lists a bunch of candidates that also does not include ushort or ulong. Again, I’m not sure what it wants.

I apologize if this is really newbish, I just don’t understand what Intellisense is telling me.

Answer 1

There’s no Sum overload which applies to a ushort sequence or to a general sequence and a projection to ushort. The simplest approach would be to simply cast to long:

return _contents.Sum(a => (long) a.Weight);

This will alleviate the overflow problem as well. Note that there is no overload using ulong either. If you have enough ushort values to overflow long, it’s probably going to take a while to add them up anyway 🙂